Car retaining cushioned latch mechanism

ABSTRACT

A cushioned latch mechanism for use with a workpiece transfer system of the type wherein a workpiece is carried along a track from one work station to another, while seated on an independently movable vehicle or carrier. The mechanism includes vehicle movement slowing and stopping means which cushions the stop of the vehicle at a work station or other predetermined position, and a latch which blocks rebound movement of the vehicle from the stop point and thereafter holds it in predetermined position. The stopping means and the latch are both mounted on a common movable member which is movable between (a) a vehicle engaging position where the stopping means and latch stop and lock the vehicle at the predetermined position, and (b) a retracted position where the stopping means and latch are moved out of the vehicle&#39;&#39;s path to permit same to proceed past the predetermined position.

United States Patent Elmore et a]. 1 Oct. 10,1972

[54] CAR RETAINING CUSHIONED LATCH 3,518,945 7/ 1970 Raney et a1..104/119 MECHANISM v [72] Inventors: Clifford L. Elmore, Cincinnati; ZKExam.lerArthur La Pomt Richard Young, Oregonia both szstantExamzner-Howard Beltran of Ohio Attorney-Wood, Herron & Evans [73]Assignee: Teledyne Mid-American Corpora- [57] ABSTRACT Los Angeles CahfA cushioned latch mechanism for use with a work- Filed: 1, 1971 piecetransfer system of the type wherein a workpiece is carried along a trackfrom one work station to [21] Appl' No" 111,332 another, while seated onan independently movable vehicle or carrier. The mechanism includesvehicle U-S. Cl. P, Q, movement slowing and stopping means 104/252,198/19 cushions the stop of the vehicle at a work station or [51] Int.Cl. ..B23q 5/22, B61k 7/08, B61k 7/18 other predetermined position and alatch whieh [58] new of Search "29/33 33 33 Q; 46/40; blocks reboundmovement of the vehicle from the 104/119 292; 198/19 stop point andthereafter holds it in predetermined position. The stopping means andthe latch are both [56] References C'ted mounted on a common movablemember which is UNITED STATES PATENTS movable between (a) a vehicleengaging position where the stopping means and latch stop and lock the642,315 1/1900 Fitton et a1. ..104/251 X vehicle at the predeterminedposition, and (b) a Baum retracted position where the stopping means andlatch 1,622,059 3/1927 Stockemer ..104/251 are moved out f the vehiclespath to permit Same to 2,729,668 12/ 1955 Bonanno ..46/40 proceed pastthe predetermined position 3,039,176 6/1962 Deschenes, ..29/33 3,343,6459/ 1967 Doerfling 198/19 13 Claims, 7 Drawing Figures PATENTEDHBI 1019123. 896, 756 sum 2 0F 3 INVENTORS W CAR RETAINING CUSHIONED LATCHMECHANISM This invention relates to a vehicle arresting mechanism and,more particularly, relates to mechanism for stopping an independentlymovable workpiece carrying vehicle at a predetermined position along apredetermined path of conveyance.

The broad concept of non-synchronous or independently moving workpiecetransfer systems is known to the art, as shown for example in Descheneset al. US. Pat. No. 3,039,176, and in Raney et al. US. Pat. No.3,518,945. Such systems basically include a series of work stationsalong a predetermined track or line along which workpieces are conveyedon individual carriages or vehicles. The work stations performoperations on the workpieces as the latter are delivered on thevehicles. The work performed may involve, for example, assemblyoperations such as welding, rivetting, bolt running; forming operationssuch as drilling or grinding, or testing.

The vehicle on which a workpiece is carried proceeds independently ofother vehicles, from one station to another; that is, the vehicles donot all move simultaneously or in synchronism, but rather start and stopdepending on their individual status. By way of example but notlimitation, one type of vehicle used in such work transfer systems is aself-propelled car guided by, and riding on, tracks as it moves from onework station to another. The vehicle may be driven by a self-containedstallable electric motor, that drives the vehicle forward whenever thecar is free to advance. The vehicle moves from an upstream stationtoward a downstream station when the work performed at the upstreamstation has been completed, without waiting for the completion of workon other workpieces on other vehicles at other stations. Such systemsoffer greatly increased assembly rate, in comparison to synchronoussystems.

Latch mechanisms by which a vehicle can be stopped and locked at apredetermined position along a guide path are, of course, known to theart, as shown in Bonanno US. Pat. No. 2,725,668, and in Doerfling US.Pat. No. 3,343,645. In many non-synchronous installations, however, itis desirable that the workpiece vehicle be stopped and secured at apredetermined position or work station very quickly after the vehiclearrives at that position. Delays in stopping or positioning the vehicleslow the rate of operation of each station. Moreover, work is oftenperformed on the workpiece while it remains on the vehicle which carriesit and thus, vehicle position determines the orientation of theworkpiece with respect to the work performing apparatus. It is thereforealso important that the vehicle be stopped and positioned quickly withinthe given tolerance limits. For example, in the case of performing adrilling operation on a part while the part is on the rates of 90 feetper minute, and even higher, are being used. At such rates, andespecially where the workpiece and/or vehicle is heavy, it is desirableor necessary to slow the vehicle gradually as it approaches a workstation, to prevent workpiece disalignment or damage by impact shock tothe workpiece or the vehicle, or to other adjacent vehicles. Thisinvention provides vehicle movement slowing and cushioning meanseffective for this purpose.

If a vehicle is stopped abruptly at a work station, there is often atendency for the vehicle to rebound or bounce back, away from the workstation. If the work operation is started during such rebound while theworkpiece is disaligned and moving, jamming, or improper workperfonnance will result. On the other hand, delay of the initiation ofthe work operation, during vehicle return to the proper position, slowsthe rate of production.

It is an advantage of this invention that is provides an economicalcushioned latch mechanism which performs all of these functions inarresting a workpiece vehicle in a work station at a predeterminedposition: namely, the function of gradually slowing or cushioning thevehicle as it is stopped in a work station; the function of accuratelylocating the vehicle as it is cushioned to a stop in the predeterminedposition, and the function of latching the vehicle in the predeterminedposition so that it cannot rebound therefrom.

In some instances it is desirable to permit a vehicle to pass through agiven work station, without stopping. This is the case, for example,when that work apparatus is not needed for the particular part beingtransported, or where no part is on the given car, having earlier beenremoved for defect or other reason. It is a further'advantage of thisinvention that the mechanism is responsive to flagging or indicatingmeans on the car, to stop the car or to permit it to pass the givenstation. Depending on whether an oncoming vehicle is to be stopped ornot, the slowing, stopping and latching mechanism is moved into or outof the path of vehicle travel, between an engaging attitude at which thevehicle isstopped and locked at a predetermined position, and aretracted attitude at which the mechanism does not engage the vehicle.

In preferred form the mechanism includes a movable bell crank whichcarries both the cushioned stopping means and a latch member which iscooperable with the stopping means. The cushioned stopping means are inthe form of a dashpot. The latch member is pivoted on the bell crank,which can be swung between a retracted position, in which both thedashpot and latch are clear of the vehicle path, and an extendedposition in which the elements can engage the vehicle as it approaches.The bell crank is operated by a piston which in turn is responsive to acontroller which senses the approach of a vehicle and which can alsosense the presence or absence of a proper workpiece on the vehicle, sothat the bell crank is moved into vehicle engaging position only when avehicle is approaching with a proper workpiece mounted on it. Optionaltiming means are provided whereby at the conclusion of a predeterminedperiod of time after vehicle arrival at the predetermined position, thepiston is pressurized to move the bell crank to retracted positionthereby releasing the vehicle and permitting it to proceed under its ownpower to the next station.

Other advantages of the invention will be more apparent from thefollowing detailed description, taken in conjunction with the drawings,in which:

FIG. I is a side elevation of a preferred form of cushioned latchmechanism in accordance with this invention, with the mechanism in theretracted attitude as a workpiece carrying vehicle is approaching themechanism from the left and travelling toward the right as shown in thefigure;

FIG. 2 is similar to FIG. 1, but illustrates the cushioned latchmechanism responding to the approach of a vehicle to be stopped, withthe mechanism now in the engaging attitude;

FIG. 3 is similar to FIG. 2 but illustrates the camming open of the'latch as the vehicle approaches more closely the slowing and stoppingmeans;

FIG. 4 is similar to FIG. 3 but illustrates the initial engagement ofthe slowing and stopping means with the vehicle, incrementally laterthan the relation shown in FIG. 3;

FIG. 5 is similar to FIG. 4 but illustrates the relation of the elementswhen the vehicle has been captured in the latched or locked attitude;

FIG. 6 is a top view taken along the line 66 of FIG. 1; and- FIG. 7 is adiagrammatic view of a control circuit for operating the mechanism.

The environment of the cushioned latch mechanism 10 of this invention isparticularly illustrated in FIGS. 1 and 6. The mechanism 10 isassociated with a workpiece transfer system (not toally shown) includinga rail or track 12, over which a workpiece vehicle or carriage 11 (notcompletely shown) moves. The track and vehicle may be of thetype'described in detail in the Raney et al patent previouslyidentified. The latch mechanism 10 is secured beside the track 12 ateach work station, at such position that the workpiece will be stoppedand locked therein by the. means to be described, in the desiredalignment with the work machinery.

Vehicle 11 rides on rollers or wheels not shown, and includes aplatform, jig or bed 14. A latch block 15 is mounted to and projectsfrom the vehicle, and is adapted to be engaged by the mechanism 10 andstopped and locked. A signal block 16 is also fixed to the vehicle, andis positioned to cooperate with a valve operator of the cushioningmeans, as will be explained. Each workpiece vehicle 11 of the system maybe similarly structured, thereby allowing each vehicle to cooperate withthe cushioned latch mechanism 10 at each work station.

Each work station may optionally include sensing means in the form ofmicroswitch 17, mounted adjacent track 12. The switch 17 has a contactoror actuating arm l8disposed to engage a workpiece, if a workpiece is infact properly oriented on the vehicle bed 14; the microswitch 17,therefore, senses whether or not a workpiece is presented for work to bedone thereon, requiring the vehicle to be stopped at the station.Asshown in FIG. 7 and described in detail subsequently, switch 17 isinterconnected with the mechanism 10 so that when the switch arm 18 isactuated by a workpiece in place on the bed 14, mechanism 10 isauthorized or permitted thereafter to engage,

The structure of the cushioned latch mechanism 10 is particularlyillustrated in FIGS. 1, 2, and 6. The mechanism includes slowing andstopping means in the form of a dashpot 20 that slows and cushionsforward motion (i.e., rightward motion as seen in the drawings) of thevehicle 11 by acting on latch block 15 as the vehicle approaches thepredetermined position. The dashpot 20 also incorporates a stop orabutment 21 that stops forward motion of latch block 15 on the vehicle11 at the predetermined position, the stop being in the form of a steelblock or, if additional cushioning is needed, a rubber bumper.

Mechanism 10 also includes a latch 22'engageable in latching relation,behind (i.e., to the left of) block 15, to restrain bounce back orrebound movement of the vehicle 11 from the predetermined position oncethe vehicle reaches that position. Once engaged, bumper stop 21 andlatch 22, in cooperation with each other, function to hold and restrainor lock the vehicle 11 at the predetermined position in the workstation, throughout the work operation carried out within that workstation.

Mechanism 10 also includes a movable member in the form of a bell crank23. One arm 24 of the bell crank mounts both the dashpot 20 and latch22. A primemover in the form of a piston 24 is pivotally connected, asat 26, with the bell cranks other arm 27. In general, the piston 25and/or dashpot may be hydraulic or pneumatic; they are illustratedherein as pneumatic. The bell crank 23 is pivotally mounted on a bracket28 by a pin 29 at its elbow 32, the bracket 28 being fixed to the baseplate 19 by bolts 33. Bell crank 23 is pivotable about the pin 29 so assimultaneously to move both the dashpot 20 and latch 22, mounted to it,between the engaging attitude (FIG. 2) where they are posi tioned forslowing, latching and locking the workpiece vehicle in the work stationatthe predetermined position, and a retracted position (FIG. 1) wherethe dashpot and latch are both removed from the path of vehicle latchblock 15 and cannot engage it, so that the vehicle can proceed throughthe work station.

Dashpot 20 includes a cylinder 36 (see FIG. 6) fixed at the end 37 ofthe bell crank arm 24. Cylinder 36 is pressurized through a restrictedorifice 38 at the downstream (rightward) end, and carries a dashpotpiston pin 39 that slides in the cylinder and is extendable upstream ofthe cylinder. The dashpot pin 39 mounts a piston 42 within the cylinder,which defines a pressure chamber 44 to the right of it. The pin 39 ismovable between an extended position (FIG. 1) when pressure fluid isadmitted to chamber 44, and a retracted position (FIG. 5) when the fluidis forcibly displaced from chamber 44 through orifice 38.

The stop or abutment block 21 is seated and mounted in a projecting lipor shoulder 48 extending upstream of the dashpot cylinder 36. Dashpotpin 39 passes centrally through the bumper 21 and projects upstream whenit is in the extended position but not when in the retracted position(compare FIG. 1 and FIG. 6).

The latch 22 includes a latch arm 51 which is pivotally mounted to thebell crank arm 24 by pin 52. A nose or catch 53 is formed at theupstream end of the latch arm 51. The latch arms nose 53 is providedwith a sloping or cam surface 50 at its leading edge for a purpose to bedescribed subsequently. A spring 54 biases or urges latch arm 51clockwise about pivot 52, toward that position illustrated in FIGS. land 2. Spring 54 is seated at its other end in bell crank arm tab 55.The spring 54, therefore, urges the latch arm.5l into an attitude wherethe rear or latch surface 56 thereof is perpendicular to the axis ofpiston pin 39, and parallel to the surface 57 of bumper block 21.

As can be seen in FIGS. 1 and ,5 the linear dimension D between thelatch arm surface 56 and the bumper block surface 57 is substantiallyequal to the length L of the latch block on the workpiece vehicle 11.Thus, when the latch block 15 is constrained or captured between bumperblock 21 and the latch 22 as illustrated in FIG. 5, the workpiecevehicle 11 is positively located andlocked in the predetermined positionat the work station.

As mentioned, the bell crank 23, and hence the combined latch 22 anddashpot structure, is moved between the vehicle engaging andvehiclepassing positionsby the piston 25. This piston includes acylinder 61 pivotally mounted by pin 62 to bracket 63. The bracket 63 isfixed to the base plate 19 by bolts 64. Piston rod 65 extends in theupstream direction from the piston cylinder 61 and is provided with atang or clevis 66 at its outer end that is pivotally linked by the pin26 with arm 27 of the bell crank 23. The inner end of the piston rod 65(see FIG. 5) is connected to a piston head 68 that divides the cylinderinto an upstream chamber 69 and a downstream chamber 71. When pressurefluid is applied to the downstream chamber 71 the rod 65 is extended,thereby causing the bell crank 23 to pivot clockwise to retractedattitude; alternately, when pressure fluid is provided to the upstreamchamber 69 the piston rod 65 is retracted, thereby causing the bellcrank 23 to pivot counterclockwise to extended attitude.

Pressure to operate piston is supplied from a pressure source 84 (seeFIG. 7) through a solenoid operated, spring return valve 85. A pressuresupply line 86 communicates between valve 85 and the upstream chamber 69of prime mover or piston 25, and a supply line 87 communicates betweenvalve 85 and the downstream piston chamber 71. The lines 86 and 87 mayinclude damping orifices designated at 88, 88 and are not shown in FIGS.l-6. In the normal position of valve 85, i.e., when the, solenoidactuator is not energized, the valve is held by its biasing spring inthe position shown in FIG. 7. Pressure air is supplied from source 84through line 87 into the chamber 71 and chamber 69 is vented at EX. Thisholds the latching mechanism 10 in the retracted attitude shown. Whenthe solenoid actuator is energized, the valve shifts, and pressure fluidis supplied through line 86 into chamber 69; the other chamber 71 isvented to exhaust through line 87, and the bell crank member is moved toextended or carrier engaging position.

A controller governs the operation of thesolenoid of valve 85, andhence, the application of pressure fluid to piston 25. Although of thoseskilled in the art will appreciate, that different controller circuitsmay be provided for different purposes, one suitable controller circuitis shown in FIG. 7 and includes the workpiece in place sensor 17. Thecontroller may also or altematively include a carrier approachingstation microswitch or sensor 89. As previously explained, the

sensor 17 is'positioned upstream of the work station, and when a carpasses is responsive to detect the presence or absence of a workpiece onthe vehicle in proper position for work to be done on it. The carapproaching sensor 89 is also positioned upstream of the station,adjacent to it, and indicates the impending approach of a car to thework station. The sensors 17 and 89 are preferably interconnected sothat both must be actuated before the solenoid of valve is energized.Thus if a car passes without a workpiece properly positioned on it,valve 85 is not shifted, and that valve is not shifted until the carrierclosely approaches a station, and passes sensor 89. (In some instancesthe two sensing functions can be combined, or one can be omitted.) Whilethe sensors are illustrated as electrically operated, they may bepneumatic. Both sensors 17 and 89 are connected to the solenoid of valve85 through a holding relay circuit 90 which maintains energization ofthe solenoid beyond the time the car passes out of engagement with thesensors.

The controller circuit is preferably also provided with a timer 91 whichregulates the duration of closure of the holding relay 90. Timer 91 maybe set for a definite period of time at station during which the car isheld for the work operation on it at the work station to be completed.When that period of time lapses the timer breaks the holding circuit andthereby deenergizes the solenoid of valve 85 so that the valve isshifted back to the position in FIG. 7. This releases the pressure inchamber 69 by venting it through line 86, and applies pressure intochamber 71 and thereby pivots the bell crank arm 23 in the clockwisedirection. Vehicle 11 is thereby released so that it may proceed out ofthe work station to move downstream.

As shown in FIG. 7, dashpot 20 is pressurized separately from piston 25.The dashpot pressurizing circuit includes a branch line 92 from pump 84.Pressure is applied to, and is released from, dashpot 20 by a cushionoperating valve means, generally at 70. Actuating means or arm 72 ispivotally mounted, as at 74, on a bracket 76 and operates a valve 75 inaccordance with the position of a vehicle. The arm 72 has a roller 77 atits end, and this roller is positioned for engagement with the signalblock 16 fixed to the workpiece vehicle. Arm 72 cooperates with andbears on a valve plunger 78 which controls the open-close operation ofvalve 75. Valve 75 is biased by spring 81 to the position shown in FIG.7. With the valve in the normal position shown, pressure air is suppliedthrough line 92 and the restricting orifice 38 to extend the dashpot pin39. The pin is normally in this extended position, ready for cushioning,when bell crank arm 23 is in the retracted position. When a car comeswithin a predetermined position upstream of the station, the block 16 onthe car comes onto and depresses valve plunger 78, thereby shiftingvalve 75. The connection between the pressure source 84 and orifice 38is broken, and orifice 38 is connected to exhaust. Orifice 38 is sizedto release or bleed off the pressure acting on the dashpot piston sothat when the piston engages the car, the dashpot piston will bedisplaced inwardly to cushion the stop at an appropriate rate. Dependingupon the size of orifice 38, it is ordinarily desirable to disconnectthe pressure source from dashpot piston just shortly before the carimpacts against the end of the dashpot pin, and the piston should remainde-energized by engagement of block 16 with, roller 77 during the entiretime the car is in station.

In operation of the cushion latch mechanism, a series of steps occurthat is sequentially illustrated in FIGS. 1-5. In FIG. 1 the mechanismis shown in the retracted attitude; it was directed to this attitudewhen the previous vehicle was released, and remains in this attitudeuntil a subsequent workpiece carrying vehicle approaches. Note thatdashpot pin 39 is extended.v As a vehicle approaches, it engages sensor89, and if a work'- piece is properly in place on the vehicle it willalso engage sensor 17; This indicates the need for a work operation tobe performed at that work station. Valve 85 is shifted and the latch anddashpot are moved to engaging position by the prime mover 25. The timerstarts timing the operation of the period that the latch arm 23 remainsin theextended position.

Just before the vehicle is to be stopped, arm 72 is depressed by thevehicle signalblock, see FIG. 2. At this time the pressure source isdisconnected from chamber of the dashpot cylinder 36. The pressure inchamber 44. starts to bleed off through orifice 38 as soon as valve 75shifts, and it is preferable to time this event (by proper positioningof block 16) so thatsufficient pressure will remain when the latch blockhits pin 39 to provide the desired rate of slowing.

As the workpiece, vehicle 11 continues to move, the latch block 15 onthe vehicle engages cam surface 50 of the latch arm nose 53 and cams ordepresses the latch arm downwardly against spring 54, see FIG. 3. Itwill be particularly noted that as this occurs block 16 on the vehicleis still depressing valve arm 72, so that no pressure is applied todashpot pin 39 which might cause sticking when the vehicle is tov bereleased.

As the latch block 15 moves into engagement with the dashpotpin 39 thepin yields in the downstream direction, slowing the vehicle andcushioning its stop. The leading face 82 of the vehicles latch block 15.engages the face 57 of bumper block 21 which positively locates thevehicle at the predetermined position. Forward momentum of the vehiclemay compress block 21 (if it is resilient), and the latch 51 snapsclockwise into latching engagement behind latch block 15 therebyrestraining the vehicle from rebounding out of the predeterminedposition. After the predetermined time interval as measured by thetimer, the solenoid of valve 85 is de-energized and valve 85 shifts, sothat the upstream chamber 69 of piston cylinder is vented and thedownstream chamber 71 is connected to the pressure .source which causespiston rod 65 to extend quickly, thereby pivoting the bell crank 23clockwise about its pivot pin.

It is important to point out that this swinging motion of the bell crankhas two effects: it withdraws the latch 22 and dashpot 20.0ut ofblocking engagement with the latch block 15, and at the same time, theswinging movement of the latch arm 23 imparts a downwardly but forwardlyangulated movement vector to the latch surface 56. Since the swing isquite rapid, the forward component of this vector'imparts a push orshove to the car, to accelerate it out of station. This gets the carstarted on its way more rapidly. The vehicle is thereafter driven by itsown motor. When the vehicle has moved out of station, spring 81 reshiftsvalve 75,

and'the dashpot is again pressurized through bleed orifice 38, so itwill be in the extended position when the next vehicle arrives. Themechanism 10 is now ready to receive a subsequent vehicle, cushion it toa stop, latch it in place and lock it positively at the work station,all as described above.

What is claimed is: i

1. A cushioned latch mechanism for use with a workpiece transfer systemof the type wherein an independently movable workpiece carrying vehiclemoves from one work station to another over a predetermined path,

said mechanism comprising,

a movable member mounted adjacent said path, said member movable betweenan extended attitude and a retracted attitudewith respect to a vehicleadjacent to it onsaid path,

resilient slowing and stopping means mounted to and moving with saidmovable member between said attitudes, said slowing and stoppingmeanswhen in said extended attitude engaging a vehicle moving along saidpath and slowing forward motion thereof as the vehicle approaches apredetermined position, said resilient slowing and stopping meansarresting forward motion of said vehicle at the predetermined position,

and a latch also mounted to and moving with said movable member betweensaid attitudes, said latch when in said extended attitude engaging saidvehicle in latching relation to block rebound movement thereof from thepredetermined position, said latch and said stopping means cooperatingto lock said vehicle in the predetermined position,

said movable member when moved from said extended attitude to saidretracted attitude disengaging said both said slowing and stopping meansand.

said latch from a vehicle and permitting a vehicle to proceed therepast.

2. A cushioned latch mechanism as set forth in claim 1 wherein saidlatch is moved by said movable member to push said vehicle out ofstation when said movable member is moved from said extended attitude tosaid retracted attitude.

3. A cushioned latch mechanism as set forth in claim 1 including acontroller responsive to the approach of said vehi-v cle toward saidcushioned latch mechanism, said controller actuating said member to movefrom the retracted attitude where said vehicle'is permitted to proceedbeyond the predetermined position, into the engaging attitude where saidstopping means and latch are positioned to stop and lock said vehicleatthe predetermined position.

4. A cushioned latch mechanism as set forth in claim 3, wherein saidlatch includes a latch arm pivoted to said member, said arm adapted torestrain said vehicle from rebounding when said vehicle is in thepredetermined position and when said member is in the engaging attitude,

bias means urging said latch arm into latching attitude. relative tosaid vehicle, and

a cam surface on said latch arm by which a latch block fixed to saidvehicle, cams and pivots said latch arm relative to said member, saidlatch block being restrained by said latch arm after said vehicle isslowed to a stop by said stopping means by biasing said latch arm intogripping relation with said latch block, thereby locking said vehicle atthe predetermined position.

5. A cushioned latch mechanism as set forth in claim 3, .wherein saidstopping means comprises a dashpot including a cylinder from which apiston pin extends, said pin being located so as to engage a vehiclewhen said member is in the engaging attitude,

a restricted orifice through which fluid escapes when said pin is pushedinto said cylinder, and

valves means for applying and releasing pressure fluid to said pistonpin,

and actuating means for operating said valve means,

according to the position of a vehicle, to apply pressure before thevehicle is at station and to release pressure when the vehicle is in thestation.

6. The cushioned latch mechanism of claim wherein said valve means bothapplies pressure to, and the releases pressure from, said piston pinthrough said restricted orifice.

7. A cushioned latch mechanism as set forth in claim 6, wherein saidstopping means and latch are mounted on one arm of a bell crank, saidlatch block being restrained between said latch arm and said stoppingmeans so as to lock said vehicle at the predetermined position.

8. A cushioned latch mechanism as set forth in claim 3, wherein areversible prime mover is connected to said member, said prime moverbeing actuable in response to said controller to move said memberrelative to the predetermined path alternatively between the engagingand retracted attitudes.

9. A cushioned latch mechanism as set forth in claim 8, wherein saidcontroller includes a timer interconnected with said prime mover, saidtimer actuating said prime mover to move said 'member into the retractedattitude after said predetermined length of time corresponding to theduration of the vehicle stop.

10. A cushioned latch mechanism as set forth in claim 8, wherein saidprime mover moves said member into the engaging attitude when theapproach of said vehicle is sensed by a sensor, and moves said memberinto the retracted attitude as determined by a time cycle set on atimer.

11. A cushioned latch mechanism as set forth in claim 8, wherein saidcontroller includes a carrier approach sensor interconnected with saidprime mover, said sensor responsive to the'approach of a vehicle alongsaid path to energize said prime mover to move said member into theengaging attitude.

12. A cushioned latch mechanism as set forth in claim 11, wherein saidprime mover includes a pressure operated piston for moving said memberalternately between the engaging and the retracted attitudes,

and wherein said mechanism also includes a valve responsive to saidcontroller to apply pressure to said piston to move said member to theengaging attitude when said sensor is actuated by the approach of saidvehicle.

13. A cushioned latch mechanism as set forth in claim 11, wherein saidcontroller further includes a second sensor, said second sensor beingresponsive to the presence or absence of a workpiece on said vehicle,said carrier approach sensor and said second sensor being interconnectedwith said prime mover to move said member to said engaging attitude whensaid second sensor senses a workpiece on said vehicle and said carrierapproach sensor senses a vehicle at a certain point on said path, and toavoid operation of said prime mover if no workpiece is on said vehicleso as to allow said vehicle to proceed past the predetermined position.

1. A cushioned latch mechanism for use with a workpiece transfer systemof the type wherein an independently movable workpiece carrying vehiclemoves from one work station to another over a predetermined path, saidmechanism comprising, a movable member mounted adjacent said path, saidmember movable between an extended attitude and a retracted attitudewith respect to a vehicle adjacent to it on said path, resilient slowingand stopping means mounted to and moving with said movable memberbetween said attitudes, said slowing and stopping means when in saidextended attitude engaging a vehicle moving along said path and slowingforward motion thereof as the vehicle approaches a predeterminedposition, said resilient slowing and stopping means arresting forwardmotion of said vehicle at the predetermined position, and a latch alsomounted to and moving with said movable member between said attitudes,said latch when in said extended attitude engaging said vehicle inlatching relation to block rebound movement thereof from thepredetermined position, said latch and said stopping means cooperatingto lock said vehicle in the predetermined position, said movable memberwhen moved from said extended attitude to said retracted attitudedisengaging said both said slowing and stopping means and said latchfrom a vehicle and permitting a vehicle to proceed therepast.
 2. Acushioned latch mechanism as set forth in claim 1 wherein said latch ismoved by said movable member to push said vehicle out of station whensaid movable member is moved from said extended attitude to saidretracted attitude.
 3. A cushioned latch mechanism as set forth in claim1 including a controller responsive to the approach of said vehicletoward said cushioned latch mechanism, said controller actuating saidmember to move from the retracted attitude where said vehicle ispermitted to proceed beyond the predetermined position, into theengaging attitude where said stopping means and latch are positioned tostop and lock said vehicle at the predetermined position.
 4. A cushionedlatch mechanism as set forth in claim 3, wherein said latch includes alatch arm pivoted to said member, said arm adApted to restrain saidvehicle from rebounding when said vehicle is in the predeterminedposition and when said member is in the engaging attitude, bias meansurging said latch arm into latching attitude relative to said vehicle,and a cam surface on said latch arm by which a latch block fixed to saidvehicle cams and pivots said latch arm relative to said member, saidlatch block being restrained by said latch arm after said vehicle isslowed to a stop by said stopping means by biasing said latch arm intogripping relation with said latch block, thereby locking said vehicle atthe predetermined position.
 5. A cushioned latch mechanism as set forthin claim 3, wherein said stopping means comprises a dashpot including acylinder from which a piston pin extends, said pin being located so asto engage a vehicle when said member is in the engaging attitude, arestricted orifice through which fluid escapes when said pin is pushedinto said cylinder, and valves means for applying and releasing pressurefluid to said piston pin, and actuating means for operating said valvemeans, according to the position of a vehicle, to apply pressure beforethe vehicle is at station and to release pressure when the vehicle is inthe station.
 6. The cushioned latch mechanism of claim 5 wherein saidvalve means both applies pressure to, and the releases pressure from,said piston pin through said restricted orifice.
 7. A cushioned latchmechanism as set forth in claim 6, wherein said stopping means and latchare mounted on one arm of a bell crank, said latch block beingrestrained between said latch arm and said stopping means so as to locksaid vehicle at the predetermined position.
 8. A cushioned latchmechanism as set forth in claim 3, wherein a reversible prime mover isconnected to said member, said prime mover being actuable in response tosaid controller to move said member relative to the predetermined pathalternatively between the engaging and retracted attitudes.
 9. Acushioned latch mechanism as set forth in claim 8, wherein saidcontroller includes a timer interconnected with said prime mover, saidtimer actuating said prime mover to move said member into the retractedattitude after said member has been in the engaging attitude for apredetermined length of time corresponding to the duration of thevehicle stop.
 10. A cushioned latch mechanism as set forth in claim 8,wherein said prime mover moves said member into the engaging attitudewhen the approach of said vehicle is sensed by a sensor, and moves saidmember into the retracted attitude as determined by a time cycle set ona timer.
 11. A cushioned latch mechanism as set forth in claim 8,wherein said controller includes a carrier approach sensorinterconnected with said prime mover, said sensor responsive to theapproach of a vehicle along said path to energize said prime mover tomove said member into the engaging attitude.
 12. A cushioned latchmechanism as set forth in claim 11, wherein said prime mover includes apressure operated piston for moving said member alternately between theengaging and the retracted attitudes, and wherein said mechanism alsoincludes a valve responsive to said controller to apply pressure to saidpiston to move said member to the engaging attitude when said sensor isactuated by the approach of said vehicle.
 13. A cushioned latchmechanism as set forth in claim 11, wherein said controller furtherincludes a second sensor, said second sensor being responsive to thepresence or absence of a workpiece on said vehicle, said carrierapproach sensor and said second sensor being interconnected with saidprime mover to move said member to said engaging attitude when saidsecond sensor senses a workpiece on said vehicle and said carrierapproach sensor senses a vehicle at a certain point on said path, and toavoid operation of said prime mover if no workpiece is on said vehicleso as to allow said vehicle to proceed past the predeTermined position.